In a previous article, Fat
Americans, we presented some information on the demographic correlates
of obesity among Americans. There are other correlates of obesity.
The following is an interview
in the magazine Hypatia with Dr. Bernardo HernŠndez Prado, a social
psychologist from UNAM Iztapalapa:

Hypatia: How did you became interested in analyzing the
effects of television in the obesity in our state?
BHP: This arises from my Ph.D. thesis theme, that addresses physical activity
and obesity in children and teenagers, mainly. With the data obtained from the
nutrition surveys, as well as some other specific studies, we made several
works. Among them you can find an investigation in Mexico City on obesity
related factors, in elementary school students. We found a very high
association between the time spent watching television and the obesity.
Recently we had the opportunity to duplicate this study in the teenage
population of Morelos, as part of a study of youth integral health,
coordinated by the INSP.

Hypatia: And what did you concluded?
BHP: Finally, we documented that the prevalence of obesity in the teenagers of
Morelos is high, it represents the 25% of its student population. This data
resembles the data obtained in Mexico City, where we found a risk factor in
the time spent watching television; and a protector factor in the physical
activity. I was amazed by the time spent watching television, according to the
survey, it ranges from 3 to 4 hours daily. The time spent in front of the T.V.
has a peak activity on weekends. Friday and Saturday are television days.

Going back to the same MARS study that was cited in our
previous article, we looked at the correlation of television viewing with
obesity. The MARS study is a general population survey of adults living in
the 50 states of the United States of America. Within this sample of
22,097 adults, 7.9% said that they are diagnosed as being obese. Among
those who are obese, their average time spent viewing television is 5.1 hours
per day; among those who are not obese, their average time spent viewing
television is 4.3 hours per day. This is a statistically significant
difference.

A visual way to present this information is through the use of
media quintiles. Here, the respondents have been sorted into quintiles
(top 20%, next 20%, ... , bottom 20%) on the basis of the amount of television
viewing per day. As shown in the first chart below, the amount of
television viewing will increase as we move up the quintiles by
definition. Then in the next chart, we show the incidences of obesity in
the same quintile groups. The incidence increases as we move up the
quintiles by definition.

Of course, we are not so naÔve as to subscribe to a theory
whereby invisible particles are emanating behind the television screen to
impinge upon the captive human audience in front of the set, thereby modifying
their metabolic processes so as to render them obese. From the same Hypatia
interview, we read:

Hypatia: What recommendations would you give to parents and
authorities on this situation?
BHP: First of all, that parents should carefully watch what their children
eat. Especially high calorie and high fat content meals. At the same time,
authorities should empower measures and policies in the selection of food
during television schedules, as well as promote sport and healthy practices
that encourage physical activity. In Cuernavaca, there aren't practically any
places where children and teenagers might practice sports; hence, improving
their overall development.

Therefore, one mechanism that explains the correlation between
television viewing and obesity is the reduced energy expenditure from the
displacement of physical activity by televising viewing. To this we can
add the increased dietary energy intake during those extended episodes of
passive television viewing. In the next chart, we show the information
from the MARS study about the incidence of obesity among people who have
participated in various leisure activities over the previous year.
Whenever the leisure activity involves significant physical exertion, the
incidence of obesity falls below the population average. An unexplored
additional mechanism is the effect of food advertising on television, which
induces over-consumption.